1. Field of the Invention
The present invention relates to a running method and a washing method for a spiral wound membrane element and a spiral wound membrane module employed for a membrane separator such as a reverse osmosis membrane separator, an ultrafiltration membrane separator or a microfiltration membrane separator as well as a treatment system employing the same and a running method therefor.
2. Description of the Prior Art
Application of membrane separation is recently spread to water purification and waste water treatment, so that membrane separation is applied to hardly treatable liquid quality. In particular, recovery and recycling of industrial waste water through membrane separation is strongly demanded.
A hollow fiber membrane element is generally employed for such membrane separation in consideration of the membrane area (volumetric efficiency) per unit volume. However, the membrane of the hollow fiber membrane element is readily broken, and raw water is disadvantageously mixed into permeate to reduce separation performance when the membrane is broken.
Therefore, application of a spiral wound membrane element in place of the hollow fiber membrane element is proposed. The spiral wound membrane element can advantageously provide a large membrane area per unit volume similarly to the hollow fiber membrane element and maintain separation performance, and has high reliability.
When waste water containing a large amount of suspended, colloidal or dissolved matter is subjected to membrane separation, the suspended, colloidal or dissolved matter is deposited on a membrane surface as contaminants to reduce the water permeation velocity. Particularly in dead end filtration, contaminants are so readily deposited on the membrane surface that the water permeation velocity is remarkably reduced and it is difficult to continue stable filtration running.
In order to prevent the membrane surface from deposition of contaminants, cross flow filtration is performed. In this cross flow filtration, raw water is fed in parallel with the membrane surface for preventing the membrane surface from deposition of contaminants through shearing force caused on the interface between the membrane surface and the fluid. In such cross flow filtration, a sufficient membrane surface linear velocity must be obtained for preventing the membrane surface from deposition of contaminants, and hence a sufficient flow rate of raw water must be fed in parallel with the membrane surface. When the flow rate of the raw water fed in parallel with the membrane surface is increased, however, the recovery per spiral wound membrane element is reduced and a large pump is required for feeding the raw water, while the system cost is remarkably increased.
On the other hand, contaminants deposited on the membrane surface may be removed by back wash reverse filtration. This back wash reverse filtration is generally performed in a hollow fiber membrane element.
For example, Japanese Patent Publication No. 6-98276 (1994) proposes application of back wash reverse filtration to a spiral wound membrane element. However, back pressure strength of a separation membrane of a conventional spiral wound membrane element is so low that the separation membrane may be broken when subjected to a back pressure in back wash reverse filtration. Therefore, the aforementioned gazette states that the spiral wound membrane element is preferably subjected to back wash reverse filtration with a low back pressure of 0.1 to 0.5 kg/cm2 (0.01 to 0.05 MPa).
According to an experiment made by the inventor, however, it was difficult to sufficiently remove contaminants when a spiral wound membrane element was subjected to back wash reverse filtration with such a back pressure, and it was impossible to maintain a high permeate flux over a long period.
The inventor has proposed a structure of and a method of preparing a separation membrane having back pressure strength of at least 2 kgf/cm2 in Japanese Patent Laying-Open No. 10-225626 (1998). However, it has not been sufficiently verified in relation to a spiral wound membrane element prepared with the separation membrane having such back pressure strength as to the level of a back pressure enabling back wash reverse filtration in practice and the range of the back pressure for back wash reverse filtration enabling the spiral wound membrane element to maintain a high permeate flux over a long period. Further, no verification has been made on a method of running a spiral wound membrane element including the aforementioned separation membrane having high back pressure strength and a method of running a spiral wound membrane module comprising such a spiral wound membrane element.
Also when the separation membrane having high back pressure strength is employed, stable filtration running cannot be performed in a spiral wound membrane element and a spiral wound membrane module without reducing the permeate flux over a long period unless optimum washing conditions and an optimum washing method are applied and the filtration running is performed by an optimum method.
An object of the present invention is to provide a running method and a washing method for a spiral wound membrane element and a spiral wound membrane module capable of performing stable filtration running at a low cost while maintaining a high permeate flux over a long period.
Another object of the present invention is to provide a treatment system employing a spiral wound membrane module allowing stable filtration running at a low cost while maintaining a high permeate flux over a long period and a method of running the same.
According to an aspect of the present invention, a method of running a spiral wound membrane element, comprising an envelope separation membrane wound on the outer peripheral surface of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, comprises a step of feeding a raw liquid containing a chemical having a contaminant separating function or a sterilizing function from at least one end of the spiral wound membrane element and taking out a permeated liquid from at least one opening end of the perforated hollow pipe in running.
In this method of running a spiral wound membrane element, a washing liquid is introduced from at least one opening end of the perforated hollow pipe in washing. The washing liquid is guided into the envelope separation membrane from the outer peripheral surface of the perforated hollow pipe, and permeated through the separation membrane in a direction opposite to that in filtration. Thus, the separation membrane is subjected to back wash reverse filtration, so that contaminants deposited on the membrane surface of the separation membrane are separated from the separation membrane.
In this case, the separation membrane of the spiral wound membrane element can be subjected to back wash reverse filtration with the back pressure higher than 0.05 MPa and not more than 0.3 MPa, whereby a necessary amount of the washing liquid can be fed in a short time. Thus, contaminants deposited on the membrane surface of the separation membrane can be effectively removed. Consequently, stable filtration running can be performed while maintaining a high permeate flux over a long period.
When a raw liquid containing a chemical having a contaminant separating function is fed into the spiral wound membrane element in the aforementioned method, contaminants can be inhibited from adhering at least to the membrane surface of the spiral wound membrane element.
When a raw liquid containing a chemical having a sterilizing function is fed into the spiral wound membrane element, bacteria such as microorganisms can be inhibited from propagating on the membrane surface of the spiral wound membrane element.
Thus, the spiral wound membrane element can be stably run over a long period.
The chemical may be sodium hypochlorite, chloramine, hydrogen peroxide, peracetic acid or ozone. Such a chemical has a function of decomposing, dissolving and separating contaminants, whereby the membrane surface of the spiral wound membrane element can be prevented from adhesion of contaminants. The membrane surface can be further prevented from propagation of bacteria due to the sterilizing function of the chemical.
The raw liquid may contain a flocculant. In this case, the flocculant flocculates contaminants contained in the raw liquid, whereby the membrane surface can readily capture contaminants, possibly passing through the membrane if the chemical contains no flocculant, due to the flocculating function. Thus, precise filtration is enabled. The contaminants captured on the membrane surface in the aforementioned manner can be discharged from the spiral wound membrane element by back wash reverse filtration with a high back pressure higher than 0.05 MPa and not more than 0.3 MPa.
The method of running a spiral wound membrane element may further comprise a step of introducing a washing liquid containing a chemical having a contaminant separating function or a sterilizing function from at least one opening end of the perforated hollow pipe and discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe from at least one end of the spiral wound membrane element in washing thereby performing back wash reverse filtration on the separation membrane with a back pressure higher than 0.05 MPa and not more than 0.3 MPa.
When the washing liquid is introduced from at least one opening end of the perforated hollow pipe, the washing liquid derived from the outer peripheral surface of the perforated hollow pipe is permeated through the separation membrane to axially flow through the spiral wound membrane element, and discharged from at least one end of the spiral wound membrane element. Therefore, contaminants captured on the membrane surface of the spiral wound membrane element, particularly in pores of the membrane, can be removed. Thus, a stable permeate flow rate can be regularly maintained when running the spiral wound membrane element.
Particularly in this case, the chemical, having a contaminant separating function, contained in the washing liquid readily removes contaminants adhering to the membrane surface of the spiral wound membrane element. Thus, the spiral wound membrane element can be effectively washed.
Further, the chemical, having a sterilizing function, contained in the washing liquid can effectively inhibit bacteria such as microorganisms from propagating on the membrane surface of the spiral wound membrane element.
Thus, the spiral wound membrane element can be stably run over a long period.
In this case, the permeated liquid may be employed as the washing liquid.
The method of running a spiral wound membrane element may further comprise a step of feeding a washing liquid containing a chemical having a contaminant separating function or a sterilizing function from at least one end of the spiral wound membrane element and axially feeding the washing liquid containing the chemical through the spiral wound membrane element in washing. In this case, contaminants adhering to the membrane surface of the spiral wound membrane element, particularly those forming a cake layer on the membrane surface can be removed. Thus, a constant permeate flow rate can be regularly maintained when running the spiral wound membrane element.
Particularly in this case, contaminants adhering to the membrane surface of the spiral wound membrane element can be readily removed due to the chemical, having a contaminant separating function, contained in the washing liquid. Thus, the spiral wound membrane element can be effectively washed.
Further, the chemical, having a sterilizing function, contained in the washing liquid can more effectively inhibit bacteria such as microorganisms from propagating on the membrane surface of the spiral wound membrane element.
Thus, the spiral wound membrane element can be stably run over a long period.
In this case, a raw liquid may be employed as the washing liquid.
The separation membrane may be formed by bonding a permeable membrane body to a surface of a porous sheet member, and the permeable membrane body may be bonded to the surface of the porous sheet member in an anchored state. In such a separation membrane, bonding between the porous sheet member and the permeable membrane body is reinforced to improve back pressure strength of the separation membrane. Thus, sufficient back wash reverse filtration can be performed with a back pressure higher than 0.05 MPa and not more than 0.3 MPa without breaking the separation membrane of the spiral wound membrane element.
In particular, back pressure strength of the separation membrane is preferably at least 0.2 MPa. Thus, back wash reverse filtration with a high back pressure is so enabled that stable membrane separation can be performed over a long period due to sufficient membrane washing.
In particular, the porous sheet member is preferably made of woven fabric, nonwoven fabric, a mesh net or a foaming sintered sheet of synthetic resin.
Further, the porous sheet member is preferably made of nonwoven fabric having a thickness of at least 0.08 mm and not more than 0.15 mm and density of at least 0.5/cm3 and not more than 0.8 g/cm3.
Thus, back pressure strength of at least 0.2 MPa can be attained, while increase of permeation resistance and separation of the permeable membrane body can be prevented while ensuring strength for serving as a reinforcing sheet.
According to another aspect of the present invention, a method of washing a spiral wound membrane element, comprising an envelope separation membrane wound on the outer peripheral surface of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, comprises a step of introducing a washing liquid containing a chemical having a contaminant separating function or a sterilizing function from at least one opening end of the perforated hollow pipe and discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe from at least one end of the spiral wound membrane element thereby performing back wash reverse filtration on the separation membrane with a back pressure higher than 0.05 MPa and not more than 0.3 MPa.
In this method of washing a spiral wound membrane element, the washing liquid introduced from at least one opening end of the perforated hollow pipe is guided into the envelope separation membrane from the outer peripheral surface of the perforated hollow pipe, and permeated through the separation membrane in a direction opposite to that in filtration. Thus, the separation membrane is subjected to back wash reverse filtration, so that contaminants deposited on the membrane surface of the separation membrane, particularly those clogging in pores of the separation membrane are separated from the separation membrane.
In this case, the spiral wound membrane element is subjected to back wash reverse filtration with the back pressure higher than 0.05 MPa and not more than 0.3 MPa, whereby a necessary amount of the washing liquid can be fed in a short time. Thus, contaminants deposited on the membrane surface of the separation membrane can be effectively removed. Consequently, stable filtration running can be performed while maintaining a high permeate flux over a long period.
When the washing liquid contains a chemical having a contaminant separating function, contaminants adhering to the membrane surface of the spiral wound membrane element, particularly those clogging in pores of the membrane can be readily removed. Thus, the spiral wound membrane element can be effectively washed.
When the washing liquid contains a chemical having a sterilizing function, bacteria such as microorganisms can be effectively inhibited from propagating on the membrane surface of the spiral wound membrane element.
Thus, the spiral wound membrane element can be stably run over a long period.
According to still another aspect of the present invention, a method of washing a spiral wound membrane element, comprising an envelope separation membrane wound on the outer peripheral surface of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, comprises a step of feeding a washing liquid containing a chemical having a contaminant separating function or a sterilizing function from at least one end of the spiral wound membrane element and axially feeding the washing liquid containing the chemical through the spiral wound membrane element.
In this method of washing a spiral wound membrane element, the separation membrane of the spiral wound membrane element can be subjected to back wash reverse filtration with the back pressure higher than 0.05 MPa and not more than 0.3 MPa, whereby a necessary amount of the washing liquid can be fed in a short time. Thus, contaminants deposited on the membrane surface of the separation membrane can be effectively removed. Consequently, stable filtration running can be performed while maintaining a high permeate flux over a long period.
In the aforementioned method of running a spiral wound membrane element, the washing liquid containing the chemical having a contaminant separating function or a sterilizing function is fed from at least one end of the spiral wound membrane element, and axially fed through the spiral wound membrane element. Therefore, contaminants adhering to the membrane surface of the spiral wound membrane element, particularly those forming a cake layer on the membrane surface can be removed. Thus, a stable permeate flow rate can be regularly maintained when running the spiral wound membrane element.
Particularly in this case, the washing liquid containing the chemical having a contaminant separating function can readily remove contaminants adhering to the membrane surface of the spiral wound membrane element. Thus, the spiral wound membrane element can be effectively washed.
When the washing liquid contains a chemical having a sterilizing function, bacteria such as microorganisms can be effectively inhibited from propagating on the membrane surface of the spiral wound membrane element.
Thus, the spiral wound membrane element can be stably run over a long period.
In this case, a raw liquid may be employed as the washing liquid.
The method of washing a spiral wound membrane element may further comprise a step of regularly or periodically feeding the washing liquid containing the chemical from at least one end of the spiral wound membrane element in parallel with back wash reverse filtration performed by introducing the washing liquid containing the chemical from at least one opening end of the perforated hollow pipe. In this case, contaminants clogging in pores of the membrane and those forming a cake layer on the membrane surface can be simultaneously and effectively removed.
The method of washing a spiral wound membrane element may further comprise a step of soaking the spiral wound membrane element in the washing liquid containing the chemical.
In this case, the washing liquid containing the chemical is introduced into the spiral wound membrane element from the perforated hollow pipe, for soaking the spiral wound membrane element in the washing liquid for a prescribed time. In a spiral wound membrane module formed by charging the spiral wound membrane element in a pressure vessel, for example, the pressure vessel is filled with the washing liquid for soaking the spiral wound membrane element therein. Thereafter the washing liquid is discharged from the system. Contaminants adhering to the membrane surface of the spiral wound membrane element can be readily removed and the spiral wound membrane element can be readily washed due to such soaking. Thus, the spiral wound membrane element can be more effectively washed. Further, bacteria such as microorganisms can be more effectively inhibited from propagating on the membrane surface of the spiral wound membrane element.
Thus, the spiral wound membrane element can be stably run over a long period.
The chemical may be sodium hypochlorite, chloramine, sulfuric acid, hydrochloric acid, nitric acid, sodium hydroxide, peracetic acid, isopropyl alcohol, oxalic acid or citric acid. Such a chemical has a contaminant separating function such as decomposition, dissolution and separation of contaminants, whereby contaminants adhering to the membrane surface of the spiral wound membrane element can be removed so that the spiral wound membrane element can be effectively washed. Further, bacteria can be effectively inhibited from propagating on the membrane surface due to the sterilizing function of the chemical.
According to a further aspect of the present invention, a method of running a spiral wound membrane module, comprising a pressure vessel having a raw liquid inlet and one or a plurality of spiral wound membrane elements stored in the pressure vessel with each spiral wound membrane element comprising an envelope separation membrane wound on the outer peripheral surface of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, comprises a step of feeding a raw liquid containing a chemical having a contaminant separating function or a sterilizing function from at least one end of the spiral wound membrane element through the raw liquid inlet of the pressure vessel and taking out a permeated liquid from at least one opening end of the perforated hollow pipe in running.
In this method of running a spiral wound membrane module, a washing liquid introduced from at least one opening end of the perforated hollow pipe is guided into the envelope separation membrane from the outer peripheral surface of the perforated hollow pipe in washing, and permeated through the separation membrane in a direction opposite to that in filtration. Thus, the separation membrane is subjected to back wash reverse filtration, so that contaminants deposited on the membrane surface of the separation membrane are separated from the separation membrane.
In this case, the separation membrane of the spiral wound membrane element can be subjected to back wash reverse filtration with the back pressure higher than 0.05 MPa and not more than 0.3 MPa, whereby a necessary amount of the washing liquid can be fed in a short time. Thus, contaminants deposited on the membrane surface of the separation membrane can be effectively removed. Consequently, stable filtration running can be performed while maintaining a high permeate flux over a long period.
In the aforementioned method of running a spiral wound membrane module, further, the raw liquid containing the chemical having a contaminant separating function is fed into the spiral wound membrane element. Thus, contaminants can be inhibited from adhering to the membrane surface of the spiral wound membrane element.
In addition, the raw liquid containing the chemical having a sterilizing function is fed into the spiral wound membrane element, whereby bacteria such as microorganisms can be inhibited from propagating on the membrane surface of the spiral wound membrane element.
Thus, the spiral wound membrane module can be stably run over a long period.
According to a further aspect of the present invention, a method of washing a spiral wound membrane module, comprising a pressure vessel and one or a plurality of spiral wound membrane elements stored in the pressure vessel with each spiral wound membrane element comprising an envelope separation membrane wound on the outer peripheral surface of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, comprises a step of introducing a washing liquid containing a chemical having a contaminant separating function or a sterilizing function from at least one opening end of the perforated hollow pipe and discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe from at least one end of the spiral wound membrane element for taking out the washing liquid from the pressure vessel thereby performing back wash reverse filtration on the separation membrane with a back pressure higher than 0.05 MPa and not more than 0.3 MPa.
According to this method of washing a spiral wound membrane module, the washing liquid introduced from at least one opening end of the perforated hollow pipe is guided into the envelope separation membrane from the outer peripheral surface of the perforated hollow pipe, and permeated through the separation membrane in a direction opposite to that in filtration. Thus, the separation membrane is subjected to back wash reverse filtration, so that contaminants deposited on the membrane surface of the separation membrane are separated from the separation membrane.
In this case, the separation membrane of the spiral wound membrane element is subjected to back wash reverse filtration with the back pressure higher than 0.05 MPa and not more than 0.3 MPa, whereby a necessary amount of the washing liquid can be fed in a short time. Thus, contaminants deposited on the membrane surface of the separation membrane can be effectively removed. Consequently, stable filtration running can be performed while maintaining a high permeate flux over a long period.
Particularly in this case, contaminants adhering to the membrane surface of the spiral wound membrane element, particularly those clogging in pores of the membrane can be readily removed due to the chemical, having a contaminant separating function, contained in the washing liquid. Thus, the spiral wound membrane element can be effectively washed.
Further, bacteria such as microorganisms can be effectively inhibited from propagating on the membrane surface of the spiral wound membrane element due to the chemical, having a sterilizing function, contained in the washing liquid.
Thus, the spiral wound membrane module can be stably run over a long period.
According to a further aspect of the present invention, a method of washing a spiral wound membrane module, comprising a pressure vessel and one or a plurality of spiral wound membrane elements stored in the pressure vessel with each spiral wound membrane element comprising an envelope separation membrane wound on the outer peripheral surface of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, comprises a step of feeding a washing liquid containing a chemical having a contaminant separating function or a sterilizing function from at least one end of the spiral wound membrane element, axially feeding the washing liquid containing the chemical through the spiral wound membrane element and taking out the washing liquid from the pressure vessel.
In this method of washing a spiral wound membrane module, the separation membrane of the spiral wound membrane element can be subjected to back wash reverse filtration with the back pressure higher than 0.05 MPa and not more than 0.3 MPa, whereby a necessary amount of the washing liquid can be fed in a short time. Thus, contaminants deposited on the membrane surface of the separation membrane can be effectively removed. Consequently, stable filtration running can be performed while maintaining a high permeate flux over a long period.
In the aforementioned method of washing a spiral wound membrane module, the washing liquid containing the chemical having a contaminant separating function or a sterilizing function is fed from at least one end of the spiral wound membrane element and axially fed through the spiral wound membrane element. Therefore, contaminants adhering to the membrane surface of the spiral wound membrane element, particularly those forming a cake layer on the membrane surface can be removed. Thus, a constant permeate flow rate can be regularly maintained when running the spiral wound membrane element.
Particularly in this case, contaminants adhering to the membrane surface of the spiral wound membrane element can be readily removed when the washing liquid contains a chemical having a contaminant separating function. Thus, the spiral wound membrane element can be effectively washed.
When the washing liquid contains a chemical having a sterilizing function, bacteria such as microorganisms can be effectively inhibited from propagating on the membrane surface of the spiral wound membrane element.
Thus, the spiral wound membrane element can be stably run over a long period.
According to a further aspect of the present invention, a method of running a spiral wound membrane element, comprising an envelope separation membrane wound on the outer peripheral surface of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, comprises a step of temporarily stopping running and holding the spiral wound membrane element in a state soaked in a liquid for a prescribed time in a running period.
In this method of running a spiral wound membrane element, contaminants adhering to the membrane surface of the spiral wound membrane element can be separated for recovering the membrane function of the spiral wound membrane element by holding the spiral wound membrane element in the state soaked in the liquid for the prescribed time. Thus, reliable and stable running can be performed. Such an operation, which can be readily performed with no requirement for particular equipment for separating the contaminants without employing a washing chemical, can be executed at a low cost.
As a first mode of the method of running a spiral wound membrane element according to this aspect, the step of temporarily stopping running may include steps of feeding a raw liquid from an end of the spiral wound membrane element and taking out a permeated liquid from at least one opening end of the perforated hollow pipe in filtration running in the running period and stopping the filtration running for holding the spiral wound membrane element in the state soaked in the liquid for the prescribed time.
In this case, the raw liquid is fed from an end of the spiral wound membrane element while filtration is performed for capturing contaminants on the membrane surface of the spiral wound membrane element.
Further, contaminants adhering to the membrane surface of the spiral wound membrane element following filtration running can be separated by stopping filtration running and soaking the spiral wound membrane element in the liquid for a prescribed time.
In the aforementioned method of running a spiral wound membrane element, part of the raw liquid may be regularly or periodically fed axially through the spiral wound membrane element. Thus, contaminants contained in the raw liquid can be inhibited from adhering to the membrane surface of the spiral wound membrane element due to shearing force acting on the membrane surface, and more stable running can be performed.
At least part of the raw liquid axially fed through the spiral wound membrane element is preferably returned to the feeding side of the spiral wound membrane element again. Thus, a permeated liquid can be obtained with high recovery by circulating the raw liquid.
As a second mode of the method of running a spiral wound membrane element according to this aspect, the step of temporarily stopping running may include steps of introducing a washing liquid from at least one opening end of the perforated hollow pipe and discharging the washing liquid from at least one end of the spiral wound membrane element thereby performing back wash reverse filtration on the separation membrane with a back pressure higher than 0.05 MPa and not more than 0.3 MPa in back wash reverse filtration in the running period and stopping the back wash reverse filtration for holding the spiral wound membrane element in the state soaked in the liquid for the prescribed time.
In back wash reverse filtration, the washing liquid is introduced from at least one opening end of the perforated hollow pipe. The washing liquid is guided into the envelope separation membrane from the outer peripheral surface of the perforated hollow pipe, and permeated through the separation membrane in a direction opposite to that in filtration. Thus, the separation membrane is subjected to back wash reverse filtration, so that contaminants deposited on the membrane surface of the separation membrane are separated from the separation membrane.
In this case, the separation membrane is subjected to back wash reverse filtration with the back pressure higher than 0.05 MPa and not more than 0.3 MPa, whereby a necessary amount of the washing liquid can be fed in a short time. Thus, contaminants deposited on the membrane surface of the separation membrane can be effectively removed. Consequently, stable filtration running can be performed while maintaining a high permeate flux over a long period also in dead end filtration readily causing deposition of contaminants on the membrane surface.
Thus, filtration can be stably performed, whereby a permeated liquid can be efficiently obtained. Further, no large pump is required for feeding the raw liquid but the scale of the system can be reduced. Thus, the system cost is reduced.
Further, contaminants adhering to the membrane surface of the spiral wound membrane element following filtration can be more effectively separated by stopping back wash reverse filtration and soaking the spiral wound membrane element in the liquid for a prescribed time.
In the aforementioned first mode, the step of temporarily stopping running may further include a step of restarting the filtration running after holding the spiral wound membrane element in the state soaked in the liquid for the prescribed time. In this case, contaminants adhering to the membrane surface of the spiral wound membrane element can be separated by soaking the spiral wound membrane element in the liquid for a prescribed time, whereby high reliability and stability can be attained in the restarted filtration running.
Alternatively, the step of temporarily stopping running may further include a step of holding the spiral wound membrane element in the state soaked in the liquid for the prescribed time and thereafter introducing a washing liquid from at least one opening end of the perforated hollow pipe and discharging the washing liquid from at least one end of the spiral wound membrane element thereby performing back wash reverse filtration on the separation membrane with a back pressure higher than 0.05 MPa and not more than 0.3 MPa. In this case, back wash reverse filtration is performed after soaking the spiral wound membrane element in the liquid for a prescribed time, whereby contaminants adhering to the membrane surface of the spiral wound membrane element can be readily and reliably separated. Thus, reliable and stable filtration running can be performed.
In the aforementioned second mode, the step of temporarily stopping running may further include a step of holding the spiral wound membrane element in the state soaked in the liquid for the prescribed time and thereafter restarting the back wash reverse filtration. In this case, back wash reverse filtration is performed after soaking the spiral wound membrane element in the liquid for a prescribed time, whereby contaminants adhering to the membrane surface of the spiral wound membrane element can be readily and reliably separated. Thus, reliable and stable filtration running can be performed.
Alternatively, the step of temporarily stopping running may further include a step of holding the spiral wound membrane element in the state soaked in the liquid for the prescribed time and thereafter feeding a raw liquid from an end of the spiral wound membrane element while taking out a permeated liquid from at least one opening end of the perforated hollow pipe thereby performing filtration running. In this case, contaminants adhering to the membrane surface of the spiral wound membrane element can be separated by soaking the spiral wound membrane element in the liquid for a prescribed time, whereby high reliability and stability can be attained in filtration running after the soaking.
In each of the aforementioned first and second modes, the step of temporarily stopping running may further include a step of holding the spiral wound membrane element in the state soaked in the liquid for the prescribed time and thereafter axially feeding a raw liquid through the spiral wound membrane element thereby performing flushing. In this case, contaminants adhering to the membrane surface of the spiral wound membrane element can be readily separated by flushing, and the contaminants separated from the spiral wound membrane element can be readily and reliably discharged.
In addition, the step of temporarily stopping running may include a step of feeding a liquid containing a chemical having a sterilizing function or a contaminant separating function into the spiral wound membrane element and soaking the spiral wound membrane element in the liquid containing the chemical. Thus, bacteria propagating on the membrane surface of the spiral wound membrane element can be sterilized, or contaminants adhering to the membrane surface of the spiral wound membrane element can be more effectively and reliably separated.
According to a further aspect of the present invention, a method of running a spiral wound membrane module, comprising a pressure vessel having a raw liquid inlet and one or a plurality of spiral wound membrane elements stored in the pressure vessel with each spiral wound membrane element comprising an envelope separation membrane wound on the outer peripheral surface of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, comprises a step of temporarily stopping running in a running period and holding the pressure vessel in a state filled with a liquid and sealed for a prescribed time.
In this method of running a spiral wound membrane module, contaminants adhering to the membrane surface of the spiral wound membrane element can be separated for recovering the membrane function of the spiral wound membrane element by sealing the pressure vessel filled with the liquid and soaking the spiral wound membrane element in the liquid. Thus, the spiral wound membrane module can be reliably and stably run. Such an operation can be readily performed with no requirement for special equipment, and can be executed at a low cost.
The liquid may contain a chemical having a sterilizing function or a contaminant separating function. Thus, bacteria propagating on the membrane surface of the spiral wound membrane element can be sterilized, or contaminants adhering to the membrane surface of the spiral wound membrane element can be more effectively and reliably separated.
The separation membrane may be formed by bonding a permeable membrane body to a surface of a porous sheet member, and the permeable membrane body may be bonded to the surface of the porous sheet member in an anchored state. In such a separation membrane, bonding between the porous sheet member and the permeable membrane body is reinforced to improve back pressure strength of the separation membrane. Thus, sufficient back wash filtration can be performed with a back pressure higher than 0.05 MPa and not more than 0.3 MPa without breaking the separation membrane of the spiral wound membrane element.
In particular, back pressure strength of the separation membrane is preferably at least 0.2 MPa. Thus, back wash reverse filtration with a high back pressure is enabled so that stable membrane separation can be performed over a long period by sufficiently washing the separation membrane.
In particular, the porous sheet member is preferably made of woven fabric, nonwoven fabric, a mesh net or a foaming sintered sheet of synthetic rein.
Further, the porous sheet member is preferably made of nonwoven fabric having a thickness of at least 0.08 mm and not more than 0.15 mm and density of at least 0.5/cm3 and not more than 0.8 g/cm3.
Thus, back pressure strength of at least 0.2 MPa can be attained, and increase of permeation resistance as well as separation of the permeable membrane body can be prevented while ensuring strength for serving as a reinforcing sheet.
According to a further aspect of the present invention, a method of running a treatment system, comprising a plurality of spiral wound membrane modules connected in parallel with each other, each comprising a pressure vessel having a raw liquid inlet and one or a plurality of spiral wound membrane elements stored in the pressure vessel with each spiral wound membrane element comprising an envelope separation membrane wound on the outer peripheral surface of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, comprises steps of feeding a raw liquid from an end of the spiral wound membrane element through the raw liquid inlet of the pressure vessel of each spiral wound membrane module and taking out a permeated liquid from the pressure vessel from at least one opening end of the perforated hollow pipe in filtration running and performing, when washing any of the plurality of spiral wound membrane modules, the filtration running on at least one of the remaining spiral wound membrane modules.
When any of the plurality of spiral wound membrane modules is washed in this method of running a treatment system, at least one of the remaining spiral wound membrane modules is subjected to filtration running, whereby the filtration running can be continuously performed. Thus, efficient running can be performed with high productivity. Further, the spiral wound membrane elements of the plurality of spiral wound membrane modules can be successively washed, whereby filtration running can be performed with a spiral wound membrane element recovering the membrane function. Thus, reliable and stable running can be performed over a long period.
This filtration running includes periodically performed back wash reverse filtration. When one of the spiral wound membrane modules is subjected to back wash reverse filtration in filtration running, therefore, one of the remaining spiral wound membrane modules may be washed. In the filtration running, however, back wash reverse filtration is performed for a short time, to hardly influence continuity of the filtration running in the treatment system.
Thus, an extremely practical and useful treatment system is implemented.
In the aforementioned treatment system, further, a raw liquid is fed from an end of the spiral wound membrane element to be subjected to filtration when the spiral wound membrane module is subjected to filtration running.
When the aforementioned spiral wound membrane module is subjected to filtration running, part of the raw liquid may be regularly or periodically fed axially through the spiral wound membrane element. Thus, contaminants contained in the raw liquid can be inhibited from adhering to the membrane surface of the spiral wound membrane element due to shearing force acting on the membrane surface, so that more stable running can be performed.
At least part of the raw liquid axially fed through the spiral wound membrane element is preferably returned to the feeding side of the spiral wound membrane element again. A permeated liquid can be obtained with high recovery by circulating the raw liquid in the aforementioned manner.
The washing may include introducing a washing liquid from at least one opening end of the perforated hollow pipe of each spiral wound membrane module and discharging the washing liquid from at least one end of the spiral wound membrane element for taking out the washing liquid from the pressure vessel thereby performing back wash reverse filtration on the separation membrane with a back pressure higher than 0.05 MPa and not more than 0.3 MPa.
When the washing liquid is introduced from at least one opening end of the perforated hollow pipe in washing, the washing liquid is guided into the envelope separation membrane from the outer peripheral surface of the perforated hollow pipe and permeated through the separation membrane in a direction opposite to that in filtration. Thus, the separation membrane is subjected to back wash reverse filtration, so that contaminants deposited on the membrane surface of the separation membrane are separated from the separation membrane.
In this case, the separation membrane is subjected to back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, whereby a necessary amount of the washing liquid can be fed in a short time. Thus, contaminants deposited on the membrane surface of the separation membrane can be effectively removed. Consequently, stable filtration running can be performed while maintaining a high permeate flux over a long period also in dead end filtration readily causing deposition of contaminants on the membrane surface.
According to the aforementioned method of running a treatment system, as hereinabove described, filtration can be so stably performed that a permeated liquid can be efficiently obtained. Further, no large pump is required for feeding a raw liquid but the scale of the system can be reduced. Thus, the system cost is reduced.
The washing may include holding the pressure vessel of each spiral wound membrane module in a state filled with the washing liquid for a prescribed time.
In this case, contaminants adhering to the membrane surface of the spiral wound membrane element can be separated for more effectively performing washing and recovering the membrane function of the spiral wound membrane element by filling the pressure vessel with the washing liquid and holding the spiral wound membrane element in a state soaked in the washing liquid. Thus, the spiral wound membrane element can be stably run over a long period.
The washing liquid may be a permeated liquid or water equivalent to a permeated liquid. Alternatively, the washing liquid may contain a chemical having a contaminant separating function or a sterilizing function. When the spiral wound membrane element is soaked in such a washing liquid, contaminants adhering to the membrane surface of the spiral wound membrane element can be separated. Particularly when the spiral wound membrane element is soaked in a washing liquid containing a chemical having a contaminant separating function or a sterilizing function, the spiral wound membrane element can be more effectively washed and bacteria such as microorganisms can be more effectively inhibited from propagating on the membrane surface.
The washing liquid may be introduced into the pressure vessel through the raw liquid inlet. Alternatively, the washing liquid may be introduced into the pressure vessel from at least one opening end of the perforated hollow pipe. Thus, the washing liquid is introduced from the raw liquid feeding side or a permeated liquid takeout side of the spiral wound membrane module, to be filled in the pressure vessel.
The method of running a treatment system may further comprise steps of connecting a raw liquid feeding pipe and a washing liquid discharge pipe to the raw liquid inlet of each spiral wound membrane module while connecting a permeated liquid takeout pipe and a washing liquid feeding pipe to at least one opening end of the perforated hollow pipe, inserting a first valve in the raw liquid feeding pipe, inserting a second valve in the washing liquid discharge pipe, inserting a third valve in the permeated liquid takeout pipe and inserting a fourth valve in the washing liquid feeding pipe, and switching the filtration running and the washing of each spiral wound membrane module through an operation of opening/closing the first, second, third and fourth valves. Thus, when any of the plurality of spiral wound membrane modules is washed, at least one of the remaining spiral wound membrane modules can be subjected to filtration running.
According to a further aspect of the present invention, a treatment system comprises a plurality of spiral wound membrane modules connected in parallel with each other, each comprising a pressure vessel and one or a plurality of spiral wound membrane elements stored in the pressure vessel with each spiral wound membrane element comprising an envelope separation membrane wound on the outer periphery of a perforated hollow pipe and allowing back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, feeding means feeding a raw liquid from an end of the spiral wound membrane element through a raw liquid inlet of the pressure vessel of each spiral wound membrane module in filtration running, takeout means taking out a permeated liquid from the pressure vessel from at least one opening end of the perforated hollow pipe in the filtration running, and passage switching means capable of switching a passage so that, when any of the plurality of spiral wound membrane modules is washed, at least one of the remaining spiral wound membrane modules is subjected to the filtration running.
When any of the plurality of spiral wound membrane modules is washed, at least one of the remaining spiral wound membrane modules is subjected to the filtration running through the passage switching means in this treatment system, whereby the filtration running can be continuously performed. Thus, efficient running can be performed with high productivity. The spiral wound membrane elements of the plurality of spiral wound membrane modules can be successively washed, whereby a spiral wound membrane element recovering the membrane function can be regularly employed for filtration running. Thus, reliable and stable running can be performed over a long period.
Therefore, an extremely practical and useful system is implemented.
In the aforementioned treatment system, the raw liquid is fed from an end of the spiral wound membrane element in filtration running of the spiral wound membrane module, to be subjected to filtration.
In filtration running of the aforementioned spiral wound membrane module, part of the raw liquid may be regularly or periodically fed axially through the spiral wound membrane element. Thus, contaminants contained in the raw liquid can be inhibited from adhering to the membrane surface of the spiral wound membrane element due to shearing force acting on the membrane surface, so that more stable running can be performed.
At least part of the raw liquid axially fed through the spiral wound membrane element is preferably returned to the feeding side of the spiral wound membrane element again. A permeated liquid can be obtained with high recovery by circulating the raw liquid in the aforementioned manner.
In washing, a washing liquid introduced from at least one opening end of the perforated hollow pipe is guided into the envelope separation membrane from the outer peripheral surface of the perforated hollow pipe, and permeated through the separation membrane in a direction opposite to that in filtration. Thus, the separation membrane is subjected to back wash reverse filtration, so that contaminants deposited on the membrane surface of the separation membrane are separated from the separation membrane.
In this case, the separation membrane is subjected to back wash reverse filtration with a back pressure higher than 0.05 MPa and not more than 0.3 MPa, whereby a necessary amount of the washing liquid can be fed in a short time. Thus, contaminants deposited on the membrane surface of the separation membrane can be effectively removed. Consequently, stable filtration running can be performed while maintaining a high permeate flux over a long period also in dead end filtration readily causing deposition of contaminants on the membrane surface.
According to the aforementioned treatment system, as hereinabove described, filtration can be so stably performed that the permeated liquid can be efficiently obtained. Further, no large pump is required for feeding the raw liquid but the scale of the system can be reduced. Thus, the system cost is reduced.
The passage switching means may include a raw liquid feeding pipe and a washing liquid discharge pipe connected to the raw liquid inlet of each spiral wound membrane module, a permeated liquid takeout pipe and a washing liquid feeding pipe connected to at least one opening end of the perforated hollow pipe, a first valve inserted in the raw liquid feeding pipe, a second valve inserted in the washing liquid discharge pipe, a third valve inserted in the permeated liquid takeout pipe and a fourth valve inserted in the washing liquid feeding pipe. Thus, when any of the plurality of spiral wound membrane modules is washed, at least one of the remaining spiral wound membrane modules can be subjected to filtration running.
Each of the first to fourth valves may be an automatic valve, and the passage switching means may further include control means controlling opening/closing each of the first to fourth automatic valves. In this case, the passage can be automatically switched by automatically opening/closing the first to fourth valves with the control means.
The control means may control the operation of opening/closing each of the first to fourth automatic valves on the basis of time setting. Thus, the passage can be automatically switched on the basis of the time setting for switching filtration running and washing at a prescribed time interval.
The control means may control the operation of opening/closing each of the first to fourth automatic valves in response to the pressure or the flow rate for feeding the raw liquid in the filtration running of each spiral wound membrane module. Alternatively, the control means may control the operation of opening/closing each of the first to fourth automatic valves in response to the pressure in the permeate liquid takeout pipe or the flow rate of the permeated liquid in the filtration running of the spiral wound membrane module. Further alternatively, the control means may control the operation of opening/closing each of the first to fourth automatic valves in response to the pressure difference between a raw liquid feeding side and a permeated liquid takeout side in the filtration running of each spiral wound membrane module. In this case, the passage can be automatically switched in response to the state of contamination of the spiral wound membrane element in the spiral wound membrane module for switching filtration running and washing.
The separation membrane may be formed by bonding a permeable membrane body to a surface of a porous sheet member, and the permeable membrane body may be bonded to the surface of the porous sheet member in an anchored state. In such a separation membrane, bonding between the porous sheet member and the permeable membrane body is reinforced to improve back pressure strength of the separation membrane. Thus, sufficient back wash reverse filtration can be performed with a back pressure higher than 0.05 MPa and not more than 0.3 MPa without breaking the separation membrane of the spiral wound membrane element.
In particular, back pressure strength of the separation membrane is preferably at least 0.2 MPa. Thus, back wash reverse filtration with a high back pressure is so enabled that stable membrane separation can be performed over a long period by sufficiently washing the separation membrane.
In particular, the porous sheet member is preferably made of woven fabric, nonwoven fabric, a mesh net or a foaming sintered body of synthetic resin.
Further, the porous sheet member is preferably made of nonwoven fabric having a thickness of at least 0.08 mm and not more than 0.15 mm and density of at least 0.5 g/cm3 and not more than 0.8 g/cm3.
Thus, back pressure strength of at least 0.2 MPa can be attained, and increase of permeation resistance as well as separation of the permeable membrane body can be prevented while ensuring strength for serving as a reinforcing sheet.